The present invention relates to a display apparatus to control two character display units of a dot matrix type and a segment type.
For instance, there are display apparatuses such as an electronic cash register which are arranged in a store or the like in which a plurality of display sections including a display section for a cashier and a display section for a customer are provided for a single information processing apparatus. Further, among such information processing apparatuses having a plurality of display sections, there is also an apparatus in which the respective display sections are constituted by different kinds of display units such as a dot matrix display unit and a seven-segment display unit. In this case, for example, the seven-segment display section is used to display a sales amount and the dot matrix display section is used to display the sales amount and transaction information.
As mentioned above, in the display apparatus of the information processing apparatus using two kinds of display units such as the dot matrix display unit and 7-segment display unit, a control circuit for controlling the dot matrix display unit and a control circuit for controlling the 7-segment display unit are independently provided as shown in FIG. 1. Namely, this display apparatus includes a display CPU 10 and a display control unit 20 which are connected to a main central processing unit (CPU) serving as an exterior controller (not shown) through a data bus 2 and a control line 3. When the display CPU 10 receives a character code transmitted from the main CPU, the CPU 10 transmits an address signal to designate the address of a character generator 11 where the dot pattern corresponding to the input character code is stored. The character generator 11 stores the shape of each character to be displayed as a dot pattern in a dot matrix formed of, e.g., five columns.times.seven rows. The character generator 11 receives the address signal and then transmits the 7-bit dot data of the respective first to fifth columns constituting the dot matrix in the designated address to five shift registers 12-1 to 12-5, respectively. The shift registers 12-1 to 12-5 each supply the 7-bit dot data of a corresponding column of the selected dot pattern as a dot drive signal to dot electrodes of a corresponding column in each display digit constituting the dot matrix display unit 14 through a driver 13.
On the other hand, in order to dynamically or time-sharingly drive the respective display digits formed of a plurality of light emitting elements of the dot matrix display unit 14 the display CPU 10 supplies a count pulse to a counter 15 synchronously with the generation of the foregoing address signal to the character generator 11. The counter 15 counts the count pulse and then supplies count data, corresponding to the count thereof, to a decoder 16. The decoder 16 sequentially supplies a digit signal, indicative of the display drive digit corresponding to the count data, to a common electrode and the selected display digit of the dot matrix display unit 14 through a digit driver 17. In this way, the respective display digits of the dot matrix display unit 14 are dynamically driven.
In addition, the display control unit 20 also connected to the main CPU (not shown) through the data bus 2 and control line 3 supplies a segment signal corresponding to the character code supplied from the main CPU to each segment electrode of each display digit constituting the 7-segment display unit 22 through a segment driver 21. On one hand, in order to dynamically or time-sharingly drive the respective display digits formed of seven segment electrodes such as LEDs or the like of the 7-segment display unit 22, the display control unit 20 supplies a scan signal to a decoder 23 synchronously with the generation of the segment signal to the 7-segment display unit 22. Whenever the decoder 23 receives the scan signal, it sequentially supplies a digit signal representative of the display drive digit to a common electrode of a corresponding digit of the 7-segment display unit 22 through a digit driver 24. In this way, the respective digits of the 7-segment display unit 22 are dynamically driven.
However, such a display apparatus in which the control circuits for controlling the dot matrix display unit 14 and the 7-segment display unit 22 are independently provided as mentioned above has the following problems. Namely, since the display units 14 and 22 for displaying characters respectively have independent display control circuits, the number of circuit parts such as IC elements and the like increases, making the whole display apparatus bulky and increasing the manufacturing costs.
On the other hand, it is necessary to respectively and independently control the display units 14 and 22, so that the control program of the main CPU has to be also constituted to respectively and independently control the dot matrix display unit 14 and 7-segment display unit 22. Therefore, there is also a problem such that the control program becomes complicated.